1. Field of the Invention
The present invention relates to a portable terminal, and, more particularly, to a vibration motor for a portable terminal capable of providing a haptic feedback function.
2. Description of the Related Art
In general, the term haptic feedback includes a driving force feedback function, such as the type used for remote control of a robot arm, and refers to a method of information feedback based on the sense of touch or user skin contact. Recently, efforts have been made to utilize haptic feedback as a vibration function to inform users of when a call is received as well as a notice function to confirm the correct signal input of a selected key when manipulating the touch screen of a portable terminal such as a cellular phone.
A portable terminal generally provides a vibration mode as one method to provide notice to users of when a call or a message is received. To perform such a vibration mode, the portable terminal is provided with a vibration motor.
In consideration of the mobility of the portable terminal, typically a coin type, a cylinder type or bar type motor is used for the vibration motor. These motor types, however, are directed to provide only the notice function of receiving a call or a message.
Recently, a touch screen phone capable of providing a full-browsing screen for using the Internet or the like has been proposed. In that regard, an input device such as a keypad is also employed as a virtual keypad presented on the touch screen. A touch screen keypad senses a spot where a person touches with a finger and inputs a signal value assigned to that corresponding spot. In contrast, a conventional button type keypad can recognize manipulations of the keypad and haptically provide users with the sense of clicking with a dome switch or the like. Accordingly, users who are familiar with keypad arrangements may realize the numbers or characters being input. On the other hand, since the keypad employed in the touch screen cannot provide the same sense of clicking as that of the dome switch, users have to directly check the value to be input through a display device.
Hence, much effort has been placed on removing the users' inconvenience to check the input value through the display device by providing a haptic feedback function to the portable terminal which employs an input device adopting a touch screen method. Such a haptic feedback function of the portable terminal can be accomplished by operating a vibration motor as a user manipulates the touch screen.
Conventional coin type or bar type vibration motors, however, have a limitation in performing the haptic feedback function because of their long response time. In other words, the coin type or bar type vibration motor has an after-vibration; that is, there is a long operation time during which the motor continues to operate due to inertia until it finally stops after the vibration motor completes its operation. Therefore, users have difficulties in haptically recognizing whether the signal value of the selected key is correctly input while making continuous key inputs at high speeds.
In the alternative, a linear motor with low power consumption and a high reliability has been proposed as a modified vibration motor with a short response time. But such a conventional linear motor has drawbacks in that it has only one value of resonant frequency. In addition, the vibration force abruptly decreases with only a slight deviation of about 2 to 3 Hz from the resonant frequency. Furthermore, the linear motor employed in the conventional portable terminal has a resonant frequency in the range from 150 to 200 Hz, and such a range of resonant frequency is enough to perform the notice function of receiving a call or message through a simple vibration movement. However, such a resonant frequency range reveals limitations in providing the haptic feedback function to acknowledge users' manipulations on the touch screen.